In the paint and coating field, the transition of dispersing media from organic solvents to water is required from the standpoint of preventing environmental pollution or insuring a safe working environment. In this regard, emulsions obtained through the emulsion polymerization of radical polymerizable vinyl monomers, as typified by acrylic resin emulsions have been widely employed as the base for a variety of paints and coating compositions because they form satisfactory coatings. Unfortunately, they essentially lack water resistance and weather resistance.
A number of attempts have been made to overcome these drawbacks. For example, emulsions are obtained through the concurrent emulsion polymerization of a vinyl polymerizable functional group-containing alkoxysilane and a radical polymerizable vinyl monomer (see JP-A 61-9463 and JP-A 8-27347). Also proposed are aqueous emulsions which are obtained by emulsifying alkoxysilane compounds or partial hydrolytic condensates thereof using various surfactants (see JP-A 58-213046, JP-A 62-197369 and JP-A 3-115485) and a system having mixed therein an emulsion obtained through the emulsion polymerization of a polymerizable vinyl monomer (see JP-A 6-344665).
However, in the former approach wherein a vinyl polymerizable functional group-containing alkoxysilane is emulsion polymerized together with a radical polymerizable vinyl monomer, more alkoxy groups are retained because of inhibited hydrolysis and it is difficult to introduce a large amount of silicone resin component in a coating. Thus important properties such as weather resistance are not improved to a level that is considered satisfactory for exterior applications. The latter approach fails to offer satisfactory coating properties because active alkoxy groups are prone to hydrolysis over time, allowing an alcohol which is an organic solvent to form as a by-product within the system, and additionally because the degree of polymerization changes with time.
As mentioned above, the prior art known methods fail to provide satisfactory coating properties. There is a desire to have an emulsion composition for building exterior walls capable of forming an elastic, flexible coating having water resistance, weather resistance, water repellency, adhesion and heat resistance and maintaining these properties over a long period of time.